Because in general propellers are bronze and shafts are iron it is conventional in shipyards to remove the propellers by a heat expansion process. Thus, typically, a propeller is manually heated with torches to expand it so that it can be dislodged from forced fit on the tapered shaft by hammering. This has several disadvantages, including energy cost, manpower cost and possible distortion of the propeller. Also, when the propellers are large it is indeed difficult to apply heat uniformly about the entire propeller hub to get the desired uniform thermal expansion characteristics.
Also, when propellers are large the forces necessary to dislodge them mechanically become very high. Cylindrical jacks about the propeller shaft may be used to dislodge the propeller from the taper fit. However, there is a break away action characteristic when the friction fit is overcome and the propeller moves on the shaft. This occurs when the jack is at maximum pressure. Thus, a hydraulic jack under high pressure instantaneously unloaded may rupture. The inertia of a heavy propeller when broken away also may cause it to damage dismount equipment.